It is known from ALL-B20144/95, regional application of a class of compounds to animals can prevent infection of ectoparasites.
However, such an application, which is for controlling ectoparasites non-systemically, was not always sufficiently quick-acting or long-lasting. For example, effective action is delayed except where applied directly. If not where applied directly, efficacy is lowered or unstable owing to bathing or washing of hair, body surface, etc.